2008 Jeep Grand Cherokee CRD
2008 Jeep Grand Cherokee CRD. Click image to enlarge

Jeep Grand Cherokee CRD – By Paul Williams

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2008 Jeep Grand Cherokee CRD

Although our series on driving style and its effect on fuel consumption started with the best of intentions, certain factors have emerged that we can’t control, and they’re having an unexpected impact on our results. All I can do at this point is relate my experience, with conclusions to come later.

The factors I’m talking about are the ambient temperature, how frequently you start and stop, the presence of deep snow on the road, getting stuck in traffic, climbing hills, and driving into a stiff wind.

You may remember that I achieved 14 litres per 100 kilometres driving “fuel-inefficiently” in our 2008 Jeep Grand Cherokee Diesel. That was mostly city driving, where Canada’s Energuide program suggests 12 L/100 km would be the norm. The temperature at the time was around the freezing point.

You might think that driving more “fuel efficiently” would generate better numbers (we certainly did!), but here’s where things came somewhat undone. Upon filling the tank and changing my driving to a more moderate, even style, the temperature plummeted from -2 to -22 degrees, and as if on cue, the biggest storm in decades arrived in town.

I remember exiting the gas station, and spending the next hour plowing through deep snow in an endless procession of vehicles trying to get home. I would reach 20-30 km/h, and then have to stop, and go, and stop. I watched with frustration as the on-board computer registered 16 L/100km. How could it not? I was using large amounts of fuel, starting and stopping, battling the snow, but making hardly any distance. If only I could get moving, I thought, I could lower my rate of fuel consumption. But I couldn’t.

Over the next few days, as Ottawa dug out, the roads across the city were unusually congested. The reason was that in many places, because of the large amounts of snow, four-lane roads were down to two lanes. Even a three-kilometre trip to the supermarket took a half-hour, and the same to return home. And it was so cold.

2008 Jeep Grand Cherokee CRD
2008 Jeep Grand Cherokee CRD. Click image to enlarge

My contact at Shell Canada tells me that while it’s true the company switches to “winter diesel” in the cold months, which is slightly less “energy dense,” this is counteracted by the fuel decreasing in volume as the temperature lowers. In effect, the reduction in volume packs more energy into a given litre of fuel. So from a fuel point of view, it shouldn’t significantly affect economy. However, there’s no doubt in my mind (with everything else being equal) that the drop to -20, -25 degrees was accompanied by an increase in fuel consumption in our Grand Cherokee Diesel.

So after 350 km of tough, cold, difficult winter driving, I was averaging about 16.5 L/100km. Maybe my fuel efficient style of driving was indeed helping, but it wasn’t being corroborated by my results in comparison to the previous tank.

I did have occasion to drive to nearby Perth, Ontario, and in combination with milder weather this made a big impact. This was a 160 km round-trip at speeds averaging 100 km/h (including some stoplights, and limited “city” driving). By the time I got home, the 16.5 L/100km reading was down to 13.2 after a total 550 km of travel. That’s better than the 14.0 L/100km I achieved driving fuel inefficiently, but not as good as expected. However, as I’ve pointed out, this was mostly very tough driving.

To further muddy the water, the next day I filled the tank and drove 60 km to Morrisburg, Ontario. Highway 31, heading south from Ottawa, is an 80 km/h zone with few stops. The temperature that day was +4 degrees, and it was raining. I set the cruise to 90 km/h and took a leisurely drive.

Well, here’s a set of circumstances that’s tough to beat: a fuel efficient driving style, comparatively warm temperature, and a steady speed on a flat road gave me 9.5 L/100 km in this heavy truck. Energuide says 9.0 L/100 km on the highway, but I don’t see how you could ever get that. To me, 9.5 L/100km (about 30 miles per imperial gallon) will be hard to beat in a four-wheel drive, 5,000 pound truck that’ll tow 7,200 pounds when asked.

The next exercise is a long drive from Ottawa to Niagara and back. This will see me travelling about 1,200 km, mostly highway, but significantly through the endless traffic jam that is Toronto (sometimes that alone can take up to two hours). The weather will be mixed, as it’s typically warmer in Niagara than up in the Ottawa Valley. The intent is to drive fuel efficiently, accurately track fuel consumption, and compare with the Energuide suggestions. Stay tuned for the outcome.

Toyota Camry Hybrid – By Grant Yoxon

2008 Toyota Camry Hybrid
2008 Toyota Camry Hybrid. Click image to enlarge

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2008 Toyota Camry Hybrid

Perhaps if I had waited a few weeks before base-lining the 2008 Toyota Camry Hybrid, I would be writing about the significant improvement in fuel economy achieved by fuel efficient driving. But instead I have to explain why, in one particularly bad week, the car used three litres per 100 kilometres more fuel than it did during the base-line week.

What I have learned during one of the worst Decembers in memory, a month of record breaking snow fall in the Ottawa region, is that environmental factors can have a significant impact on fuel consumption. I also came to realize that the type of driving one does can have a greater impact on fuel consumption than one’s driving style.

As I said, let me explain…

When we began this exercise, we agreed to use fuel efficient driving techniques: no warm-ups, no idling, and no jack-rabbit acceleration. We would drive at the speed limit, keep a light foot on the accelerator and, in my case, use whatever techniques seemed to work to maximize driving in electric-only mode.

However, the Camry Hybrid does not go into full electric mode, in which the gasoline engine shuts down completely during deceleration, driving at slow speeds or at a full stop, until the engine and the car is fully warmed up. If the driving routine involves a lot of short trips, it is very difficult to conserve fuel.

Combine this with low ambient temperatures, snow clogged streets, a pre-driving warm-up made necessary by an accumulation of ice and snow and the best intentions go right out the window. The result, during one week of short hop city driving and several days of alternating freezing rain and heavy snow, was 10.7 L/100 km, nearly 3 L/100 km more than the baseline 7.8 L/100 km recorded during the relatively balmy baseline week in November and nearly doubling the Energuide rating (5.7 L/100 km in both city and highway driving).

That was the worst. But I suspect that the hybrid was no different than any other vehicle in adverse conditions – when the going gets tough, the fuel gets flowing.

2008 Jeep Grand Cherokee CRD
2008 Jeep Grand Cherokee CRD. Click image to enlarge

Give the Hybrid some time, though, and even in bad weather, the fuel consumption drops. The week before Christmas was a good example. After several short trips to the mall, the Camry was registering 8.7 L/100 km according to the on-board driver information centre. After two trips to the north end of Gatineau from the east end of Ottawa, during which I became manic about getting the fuel consumption down, fuel use dropped to 7.2 L/100 km. And the next day, after a highway trip south to Winchester and a fill up, the car was logging 6.9 L/100 km.

The best I could do, during a highway trip to Toronto and back – yes, you can drive from Ottawa to Toronto and back on one tank of fuel – was 6.2 L/100 km. Still off the Energuide rating of 5.7 L/100 km but not bad considering the roads were partially snow covered, the Camry is wearing snow tires which increase rolling resistance, and the car was carrying several hundred pounds of passengers and luggage.

While it is difficult to separate the effects of fuel efficient driving techniques from other, mostly adverse, factors affecting fuel consumption, my fuel log shows that with the exception of one tank of fuel – the 10.7 tank – all have been less than the baseline of 7.8 L/100 km. I’ve filled up the Camry six times so far and recorded a 7.7, 7.6, 6.9 and 6.2 in addition to the 7.8 baseline and the 10.7 week from hell.

Along the way, I’ve learned a few techniques to get the fuel consumption down. I pace myself to maximize green lights and plan routes that avoid stop signs. Acceleration is the enemy of fuel conservation. I begin deceleration for a traffic light or stop sign as early as possible to conserve fuel and recharge the batteries. On city streets, I keep the speed below 62 km/h, the point at which the gasoline engine will shut down. And I encourage electric mode driving by lightly lifting my foot off the accelerator, prompting engine shutdown and electric mode driving.

But I’ve also learned that one must drive the Camry Hybrid to achieve the best fuel economy. Given that our goal is to reduce fuel consumption, it is ironic that you have to use fuel to save fuel.

More Fuel Economy Challenge articles:
Introduction | December 11 update | Conclusion, Part One

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